Configuring addresses in a communication network

ABSTRACT

The present invention relates to a method for configuring addresses in a packet switched data communication system. The method comprises providing a logical network with at least two network elements, a network element comprising at least one sub-element. The method further comprises configuring a temporary address for an interface of a sub-element, retrieving an identifier of the network element and defining an address for the interface of the sub-element by including the identifier of the network element to the temporary address.

FIELD OF THE INVENTION

The invention relates to communication systems, and more particularly toconfiguring addresses in a packet switched communication system forcommunication network elements, such as telecommunication equipment.

BACKGROUND OF THE INVENTION

A communication system can be seen as a facility that enablescommunications between two or more entities such as user equipmentand/or other network elements, also called nodes, associated with thecommunication system. A communication system typically operates inaccordance with a given standard or specification which sets out whatthe various entities associated with the communication system arepermitted to do and how that should be achieved.

Examples of communication systems may include fixed communicationsystems, such as a public switched telephone network (PSTN), wirelesscommunication systems, such as a public land mobile network (PLMN),and/or other communication networks such as an Internet protocol (IP)transport network and/or other packet switched data networks. Variouscommunication systems may simultaneously be concerned in a connection.

Wireless communication systems include various cellular or otherwisemobile communication systems using radio frequencies for sending voiceor data between stations, such as user equipment (UE) (e.g. mobilestations, MS) and base transceiver stations (BTS), also called basestations. Examples of mobile communication systems are the global systemfor mobile communications (GSM), general packet radio service (GPRS) andthe so-called third generation (3G) mobile communication systems, suchas the universal mobile telecommunications system (UMTS) terrestrialradio access network (UTRAN).

An example of the IP transport network is the Internet, which is aglobal network formed by the interconnection of numerous smallernetworks all adapted to use the Internet protocols, such as the InternetProtocol (IP) and the Transmission Control Protocol (TCP), and a commonaddress structure. In addition to said protocols, the IP transportnetwork may include a number of auxiliary protocols, such as the addressresolution protocol (ARP), open shortest path first (OSPF) and Internetcontrol message protocol (ICMP). The IP transport network providestransfer of data in links provided between nodes, i.e. hosts androuters, within and between the smaller networks.

The IP network operates according to a principle of layeredcommunication, where lower layers serve upper layers and adjacent layerscommunicate over an interface. An example of a layered communicationmodel is the Open System Interface (OSI) reference model. The layers ofthe OSI reference model may be called the physical layer (the firstlayer), the data link layer (the second layer), the network layer (thethird layer), the transport layer (the fourth layer) and the applicationlayer (the fifth layer).

The data link layer (i.e. the second layer, L2) controls data flow,handles transmission errors, provides physical addressing and managesaccess to the physical medium. In the data link layer, data link layerdevices, such as bridges and switches, take care of these functions. Thedata link layer may use Ethernet protocol, for example.

The network layer takes care of routing, i.e. determining optimalrouting paths and transferring the data packets over the IP network froman originating party, i.e. source host, to a terminating party, i.e.destination host. In determining optimal routing paths, the networklayer may use routing algorithms and routing tables. A routing pathtypically goes through routers. The network layer transfers informationusing so-called protocol address of the terminating party in determiningthe physical addresses of the routers along the routing path. In thenetwork layer, the IP version 4 protocol (IPv4) or the IP version 6protocol (IPv6) may be used. Other protocols may also be used. Examplesof such protocols may include the IPX, NetBIOS, DECnet, SNA, AppleTalkand so on.

In an IP network each node, including hosts and routers, has an address,which is unique for the element. The Internet Engineering Task Force(IETF) has developed an addressing architecture of the IP for assigningidentifiers for node interfaces. A single interface of a node has atleast one IP address, but may have multiple IP addresses as well.

Both the IPv4 and the IPv6 provide a structure for defining the IPaddresses. The IPv4 defines addresses of 32 bits and the IPv6 increasesthe address size to 128 bits. The IP address consists of two parts: thenetwork portion and the host portion. The network portion identifies thenetwork to which the node is connected and may also be called a subnetprefix. The host portion identifies the host in the network, or in otherwords, the interface on which the host is attached to the link. In theIPv6, the host portion is called as an interface identifier (interfaceID).

In the IPv4, the number of addresses is limited and a careful addressplanning is needed. Gateways (i.e. IP Routers) are typically used tocreate addressing structure where a private network has an independentprivate address space (intranet) and only a limited amount of publicaddresses. The DHCP (Dynamic Host Configuration Protocol) is appliedusually for autoconfiguring IP addresses and other network settings tothe IPv4 hosts.

In the IPv6, there are much more available IP addresses than in theIPv4. An IPv6 address consists of 64-bit long prefix portion and 64-bitlong interface ID portion. The IPv6 incorporates also site-locally andlink-locally scoped addresses in addition to the globally routableaddresses. Site-locally scoped addresses are used for communicationsinside private networks as these addresses shall not route outside thedefined boundary. Link-locally scoped addresses are used forcommunications between nodes that are connected to the same link i.e. amedium over which nodes can communicate at the link layer. Example ofsuch a link is a simple or bridged Ethernet. An IPv6 node may assign toits interface IPv6 addresses with multiple scopes depending on itscommunication needs with other nodes that may reside in the same link,site, or in some other public IPv6 network. The scoped IPv6 addressesare formed so that the same interface ID portion is joined withdifferent prefix portions that are defined for each scope.

In the IPv6, an address autoconfiguration process is provided formulticast-capable links. In the autoconfiguration, a node, i.e. a hostor a router, generates a preliminary, also called tentative, link-localaddress by appending the interface ID to a known link-local prefix. Anaddress is tentative until its uniqueness is verified. The node verifiesthe uniqueness of the tentative link-local address by making enquiriesin the neighboring nodes. If the verification shows that the tentativeaddress is unique, said address is assigned to the interface. If theverification shows that the address is already used by another node,there may be an alternative interface ID to be tried or a manualconfiguration may be required. A host may then receive furtherinformation from a router and may continue its autoconfiguration basedon this information.

The mobile communication networks as defined by the third generationpartnership project (3GPP) are expected to apply IP transport option inradio access networks (RAN), for example in the UTRAN. FIG. 1 shows anexemplifying architecture for the IP transport network 1, i.e. IPnetwork of routers, as defined by the 3GPP. A router 16, 18, 44connecting a host, such as a transceiver network element, e.g. a Node B12, 14, or a controller network element, e.g. radio network controller(RNC) 42, to the IP network 1 may be called an Edge Router. Typically,each Node B and RNC 12, 14, 42 needs its own router 16, 18, 44 toconnect the Node B 12, 14 and the RNC 42 with the IP network 1. In somecases, two or more network elements, such as two or more transceivernetwork elements, such as two or more Node Bs 22, 24, or a transceivernetwork element, such as a Node B 32, and a controller network element,such as a RNC 34, may be directly connected to each other with apoint-to-point link. This connection takes no benefit from the IPinfrastructure and no intermediate router is needed between the twotransceiver network elements 22, 24 or 32, 34. Each network elementremains an individual IP node.

It shall be appreciated that FIG. 1 is only an example of a simplifiedIP transport network. The number, type and order of the entities maydiffer substantially from the shown. It shall also be appreciated thatthe terms used in the context of FIG. 1 refer to the 3G mobilecommunication system as defined by the 3GPP. In the second generation(2G) mobile communication systems, such as the GSM, the transceivernetwork element is typically called a base transceiver station (BTS) orsimply base station and a controller network element is typically calleda base station controller (BSC).

When IP transport is applied in the radio access network, it is obviousthat the base stations become IP nodes that may build up an internallocal area network (LAN), based for example on the Ethernet protocol.This is shown in FIG. 2, where a base station node 200 is build ofmultiple base station modules each comprising an IP host connected tothe internal LAN 210 of the base station node. The base station node 200may be a telecommunication equipment comprising a cabinet housingmultiple base station hardware modules 204, 205, 206, 207 that togetherimplement for example the Node B functionality according to the 3GPPspecifications. The base station modules may typically be replaceableplug-in units. The base station node may sometimes be also called a basestation cabinet as often a logical base station fits into a singlephysical equipment, i.e. the cabinet.

The FIG. 2 arrangement is similar to the ensemble of Node Bs 12, 14 andEdge Routers 16, 18 of FIG. 1 corresponding to the base station nodes200, 250 and IP routers 203, 253 of FIG. 2, respectively. As shown inFIG. 2, the IP router 203 as a network layer forwarding deviceseparates, or isolates the base station internal IP subnet and EthernetLAN from other networks, such as the external IP transport network, allthe traffic that happens just between the base station internal modules.Therefore, instead of using globally unique Ethernet addresses, the basestation modules may assign dynamically (autoconfigure) locally scopedEthernet addresses to be used for the base station internalcommunications at the link layer.

One physical transport module of the base station may include both theIP router and L2 switch functions. Alternatively, the IP router functionmay be implemented by a separate, base station external physical device,into which the base station is connected. In such a case, the transportmodule may contain only the L2 switch function.

One of the base station modules is a transport module 202 connected withan IP router 203 and connecting the base station internal LAN 210 to theexternal IP transport network 1 of the radio access network (e.g.UTRAN). The IP router 203 provides a default gateway function to thebase station modules 204, 205, 206, 207 comprising IP hosts. Theinternal LAN 210 of the base station node 200 forms a single IP subnetconfigured in the IP router 203 and the base station modules 204, 205,206, 207 share the same IP subnet prefix for communicating outside theinternal LAN 210. As several base station modules may be included ineach base station node, and each base station module may represent oneor more IP hosts, a base station node as a network element may requireeasily tens of Ethernet and IP addresses.

If two or more base station nodes 200, 250 need to be connected to theIP transport network 1, each base station node 200, 250 needs an IProuter 203, 253, as shown in FIG. 2. Each base station node 200, 250thus forms its own internal LAN 210, 260 and has its own IP subnetprefix.

The amount of required IP subnets increase when all the base stationnodes are interconnected using an IP routed network. In the FIG. 1architecture, each Node B represents one IP subnet that has to beadvertised using routing protocols to other routes in the IP network.The amount of required public IP addresses in each IP subnet depends onhow many IP hosts in the base station nodes has to be able tocommunicate with IP hosts connected to the base station external IPnetworks. Thus, the amount of addresses towards the external IP networkincreases quickly.

Therefore, there is a need for alternative ways of configuration of IPaddresses.

SUMMARY OF THE INVENTION

Embodiments of the invention aim to address one or several of the aboveproblems or issues.

In accordance with an aspect of the invention, there is provided amethod for configuring addresses in a packet switched data communicationsystem, the method comprising providing a logical network with at leasttwo network elements, a network element comprising at least onesub-element, configuring a temporary address for an interface of asub-element, retrieving an identifier of the network element anddefining an address for the interface of the sub-element by includingthe identifier of the network element to the temporary address.

In accordance with another aspect of the invention, there is provided anetwork element comprising at least one sub-element, a configuring meansadapted to configure a temporary address for an interface of asub-element and to define an address for the interface of thesub-element by including an identifier of the network element retrievedby a retrieving means and the retrieving means adapted to retrieve theidentifier of the network element.

In accordance with another aspect of the invention, there is provided acommunication system comprising a logical network comprising at leasttwo network elements, a network element comprising at least onesub-element, a configuring means adapted to configure a temporaryaddress for an interface of a sub-element and to define an address forthe interface of the sub-element by including an identifier of thenetwork element retrieved by a retrieving means and the retrieving meansadapted to retrieve the identifier of the network element.

BRIEF DESCRIPTION OF FIGURES

The invention will now be described in further detail, by way of exampleonly, with reference to the following examples and accompanyingdrawings, in which:

FIG. 1 shows an example of architecture for an IP transport network inwhich embodiments of the invention may be implemented;

FIG. 2 shows multiple base stations connected to the IP transportnetwork according to an implementation of the prior art;

FIG. 3 shows multiple base stations connected to a logical networkaccording to an embodiment of the invention;

FIG. 4 is a flow chart illustrating an embodiment of the invention;

FIGS. 5 a-5 c show Ethernet and local-use address formats in the basestations according to an embodiment of the invention;

FIG. 6 shows an example of the BTS control module IPv6 addressautoconfiguration procedure according to an embodiment;

FIG. 7 shows an example of another BTS module IPv6 addressautoconfiguration procedure according to an embodiment making use of theresult from the FIG. 6 embodiment;

FIG. 8 shows an example of a BTS module IPv4 address autoconfigurationprocedure according to a further embodiment; and

FIG. 9 shows an example of discovery of the node information accordingto an embodiment making use of the result from the FIG. 8 embodiment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Embodiments of the present invention are described referring mainly tothe base station node and 3GPP specifications, but the same idea may beimplemented with any telecommunication equipment with similarcharacteristics as well.

In accordance with the embodiments of the invention, connecting multiplenetwork elements comprising sub-elements to a single logical network, orsubnetwork, is enabled. A single logical network may be, for example, asingle logical LAN having only one IP router towards the external IPnetwork. An example of a preferred embodiment may be connecting multiplebase stations or base station nodes comprising base station modules to asingle second layer (L2), i.e. link layer, switched network instead ofconnecting the base stations or base station nodes into separate IPsubnetworks each connected via a separate IP router with the external IPnetwork.

Connecting multiple base station nodes to the same logical LAN may bedesirable, for example, for extending base station radio capacity bychaining two or more base station nodes into one logical base stationsystem. In accordance with an embodiment, the base station nodes locatedphysically close to each other may be bridged together using L2switches. One of the base station nodes may become “Master”, which hasthe IP router function for interconnection to the IP transport network.The other base station node(s) then become “Slaves” providing hardwareand software for radio capacity extension.

Another example may be reducing the amount of routers in the IPtransport network. For example, the OSPF protocol has limitations forthe maximum number of routers in the routing areas. A group of basestations located close to each other may be interconnected using abridged, i.e. L2 switched, transport solution. The interconnected basestation nodes may serve, in some cases, as separate base station nodesor, in some cases, as a chained base station.

An embodiment of the invention is shown in FIG. 3. In the FIG. 3embodiment, two base station nodes 300, 350 are bridged together to forma logical network 310. The logical network 310 appears to the IP network1 as one IP subnet. The base station nodes 300, 350 each comprise a basestation control module 304, 354 and other base station modules, such asbase station baseband modules 305, 306, 355, 356 and RF (radiofrequency) modules 307, 357. The other base station modules 305, 306,307, and respectively 355, 356, 357, should have some means to discoverthe correct base station control module 304, and respectively 354,residing in the same base station node 300, and respectively 350, inorder to select the correct Cabinet ID to be used in the addresses ofsaid other base station modules.

When multiple base stations are to be connected to the L2 switchednetwork, all the base station modules 304-307 and 354-357 in basestation nodes 300 and 350 can communicate with each other using justlocal-use IP addresses, such as IPv6 link-local or private IPv4addresses. This is possible, because the base station modules areconnected to the same logical LAN now.

In this kind of an environment, multiple base station nodes have toshare the same IP subnet prefix. Now if the base stations create theirlink layer or IP addresses for the modules with node-local scope, forexample, based on the module hardware position, the addresses in thebase station nodes will overlap. It has now been found that anadditional identifier for the base station node could be added in theaddresses in order to create unique addresses within the scope of theshared IP subnet and logical LAN. In the examples below, the additionalidentifier identifying a base station node shall be called a CabinetIdentifier (Cabinet ID). The use of the Cabinet ID in the addressesguarantees the uniqueness of the module addresses in each base stationnode that is connected to the single logical network, such as the samelogical L2 switched LAN. In order to keep the base station configurablewith minimum effort, it may be desirable in certain embodiments to avoidintroducing more manually configurable parameters. Thus, also theCabinet ID should be autoconfigurable.

The logical Ethernet LAN 310 provides a location independent networkfrom addressing point of view, i.e. nodes could be connected to anyavailable physical interface of the LAN and they could use the same linklayer and IP addresses for communications all the time. The onlyrequirement for the used addresses is that they are unique within thescope of the LAN. The L2 switches (and bridges) maintain forwardingtables automatically based on ongoing traffic at link layer. Theforwarding table binds the detected link layer addresses to ports(physical interfaces) of a L2 switch. Now in theory, it could bepossible to resolve the topology of the LAN and the physical locationsof the nodes with accuracy of a port just based on information in theforwarding tables. However, ordinary nodes of the network cannot, or arenot allowed to access the contents of the forwarding tables from the L2switches. Actually, if there is interface available for reading thisinformation, it is usually limited to be accessed only via the networkmanagement system. Thus an ordinary node has no means for resolving itsown, or other node's physical location in the topology of a L2 switchedLAN.

In an embodiment, the base station modules are made capable ofdiscovering automatically the Cabinet ID of the base station node, inwhich the modules are located physically. This discovery process canoccur during the initial startup of the base station node, or during a“hot-insert” of a base station module, i.e. inserting a module into thebase station node during its normal operation without switching off thepower. Such a real-time discovery of the Cabinet ID must avoid usingoverlapping addresses even temporarily. Typically, during the initialbase station startup, only the base station control module has access tothe Cabinet ID information, which may, for example, be stored in anon-volatile memory of the base station control module. Thus, only thebase station control module is capable of creating link layer addressand IPv6 Interface ID so that the addresses contain unique CabinetIdentifier Information i.e. have wider scope than a single base stationnode. All the other base station modules must then resolve theirphysical location and Cabinet ID by discovering the correct base stationcontrol module over the Ethernet connections. The problem is that whenmultiple base station nodes are connected to the same logical L2switched LAN, the base station modules would normally receive responsesto their discovery messages from multiple base station nodes withoutbeing able to resolve automatically in which of the responding basestation nodes the base station module itself is located physically.

The embodiments of the invention allow connecting multiple IP basestation nodes to a L2 switched network without manual configuration of aCabinet ID, link layer addresses (Ethernet MAC) and IP addresses intothe base station modules in advance. Also the base station modules canbe hot-inserted into an operational base station node without manualconfiguration in such environment.

In the embodiments of the invention, instead of using the usual globallyunique Ethernet MAC addresses, the base station modules can usedynamically created addresses that are configured e.g. based on thehardware location information of a sub-element, such as the base stationmodule, and including an identifier of the network element, such as theCabinet ID. The dynamically created Ethernet MAC addresses need to beunique only within the scope of the local area network (LAN). Also thenetwork layer IPv6 addresses can be derived from these dynamicallycreated Ethernet MAC addresses as specified in the document RFC 2373 “IPVersion 6 Addressing Architecture”. The network layer IPv4 addresses canbe configured automatically by using a dynamic host configurationprotocol (DHCP) server that may be located in the IP Router of the rootbase station 300.

In general, the method embodying the invention may be used for anycommunication network element having an internal local network, whichmay become part of an external IP transport network. FIG. 4 shows thesteps of an embodiment as a flow chart. In step 400, a logical networkis provided with at least two network elements, wherein a networkelement comprises at least one sub-element. In step 402, a temporaryaddress is configured for an interface of a sub-element. The address maybe configured for the link layer, for example, based on the hardwarelocation information of the sub-element in the network element or basedon a module identifier of the sub-element. In step 404, an identifier ofthe network element is retrieved. In step 406, an address for theinterface of the sub-element is defined by including the identifier ofthe network element to the temporary address.

Some embodiments of the invention will be described in the following byway of examples.

In an embodiment, the base station modules create dynamically thelocal-use addresses to be used for communications within the scope ofthe local area network, such as link layer (e.g. Ethernet) and networklayer (e.g. link local IPv6) addresses, for example in the formatillustrated in FIGS. 5 a, 5 b and 5 c. Field lengths in FIGS. 5 a, 5 band 5 c are shown in bits. Each IP host in the base station modulesassigns a link layer address that is unique at least inside the LAN thata base station node is going to build up. The link layer address (LLA),such as the 48-bit Ethernet MAC address is preferably based on hardware(HW) position information of the module when possible. Alternatively,for example if the module HW position information is not available ormay otherwise not be used, the link layer address may be based on aserial number of the module.

FIG. 5 a shows an example of a MAC address based on the HW position ofthe module. A factory loaded boot software of each processor is capableto create its own link layer address based on an identifier of theprocessor, such as a Processor ID (IF ID) inside the module, and on anidentifier of the physical position ID that is readable automaticallye.g. via I/O pins in the hardware of the node (such as a Subrack ID,Slot ID).

When the 48-bit MAC address is created based on module HW position,there may be, for example, 33 (i.e. 5+28) bits reserved for a Cabinet ID(“Cab” and “Cabinet” in FIG. 5 a). The 12 last bits may be used for theSubrack ID, Slot ID, and IF ID. The xug bits are filled as follows: “x”defines address allocation method and may be 0 indicating a HW positioncase; “u” is a universal/local bit and may be 1 indicating local scope;and “g” is an individual/group bit and may be 0 indicating individualaddress. The “u” and “g” bits are typically defined by the Institute ofElectrical and Electronics Engineers (IEEE). The “x” bit is proprietary.

FIG. 5 b shows an example when the module is not able to read itsposition information and the serial number of the module may be used.The serial number of the module may, for example, consist of thefollowing fields: FF is a factory symbol, YY is the production year(e.g. 0-99), WW is the production week (e.g. 01-52) and NNNN is aconsecutive running reference number (e.g. 00001-99999). The xug bitsmay be set as in the above HW position embodiment except that the “x”bit is set to 1 to indicate that a serial number allocation method isconcerned. If the module has several processors but only one serialnumber, the IF ID may be used to separate processors.

FIG. 5 c shows an example of the structure of local-use addresses,so-called unicast link local IPv6 addresses, which are used inside thebase station node. The addresses shall begin with a binary prefix1111111010 and comprise a 64-bit interface ID portion. The interface IDmay be used by the base station modules for internal communication andfor communication towards the router. The base station modules maygenerate the interface ID according to the document RFC2464“Transmission of IPv6 Packets over Ethernet Networks” based on theEUI-64 identifier. This means that the 48-bit MAC address is taken asthe basis and fixed value FFFE is added in the middle. It is to be notedthat, when creating the interface ID, the “u” bit is inverted to 1 inthe address to indicate universal scope.

The nodes that are addressed link-locally, are able to communicate withneighbors in the same link (e.g. Ethernet LAN) through this addressingscheme. It is to be noted that routers do not forward any packets withlink-local source or destination addresses to other links. The IPv6 linklocal addressing and stateless address configuration may ensure that aBTS node is capable of establishing internal communication between allthe modules without any manual configuration. Following from the above,the interface ID is allocated based on the HW address of the module,such as the HW position, or based on module's unique serial number. Thisallocation mechanism allows every host to obtain a unique IP addresswithout fear of overlapping addresses.

Link Layer Addresses

The dynamic creation of the link layer addresses may be based on theIEEE 48-bit MAC Identifier format as defined by the IEEE.

The 48-bit MAC Identifiers may have the “universal/local” and“individual/group” bits set fixed to zeroes in order to limit the scopeof the addresses to a local use, and to provide unicast type addressesfor the interfaces. As the scope of the addresses is local, the 48-bitMAC Identifiers need not to apply officially assigned “company id” bits(c-bits) i.e. these bits can be used freely also for other purposes e.g.for the most significant bits (MSBs) of the Cabinet ID information as inthe example address that is shown in FIGS. 5 a-5 c.

The contents of the manufacturer selected extension identifier (24 leastsignificant bits (LSBs), known as “m-bits”) may be derived from the HWposition (Interface ID, Slot Position and Rack Position) and Cabinet IDinformation. In an alternative embodiment, for example if the HWposition information is not available, the bits for this field may bederived from a module identifier, e.g. from the module serial number.

Link-Local IPv6 Addresses

All the base station modules shall create dynamically their link-localIPv6 addresses based on the EUI-64 identifier that is derived from theIEEE 48-bit MAC Identifier. The creation of link-local IPv6 address isspecified in the document RFC 2373 “IP Version 6 AddressingArchitecture”.

The base station Control Module shall assign also a “well known”link-local IPv6 address for its OA&M (Operations, Administration &Maintenance) interface that will be used for the Cabinet ID discoverypurposes. This address can be in principle any link-local IPv6 addressthat is reserved only for this purpose.

Considerations for Address Autoconfiguration in a L2 Switched Network

Referring back to FIG. 3, an example of an arrangement of multiple basestations in a L2 switched network is shown. Multiple IP base stationnodes 300, 350 are connected to a L2 switched LAN 310. The logicalnetwork 310 extends thus to cover multiple base station nodes 300, 350each representing their own LAN segment. In the embodiment of thisinvention, it is assumed that the L2 switches in the base stationtransport modules 302 and 352 are capable to support VLAN (Virtual LAN)according to IEEE 802.1Q specification “Virtual Bridged Local AreaNetworks”.

The base station address autoconfiguration during the initial startupwill work without overlapping address problems in a L2 switched network310 if the following conditions are met. The reference numerals usedbelow refer only to the base station node 300, i.e. one of the LANsegments. This is done for clarity. The same conditions apply for theother base station node 350, or other base station nodes, in order toautoconfigurate the whole logical network, i.e. the L2 switched LAN 310.

-   -   1. A base station transport module 302 included in the base        station node 300 does not enable the external interfaces of the        base station transport module 302 if no valid configuration data        (e.g. commissioning file) has been received. Only exception is a        local management port which interface is required for connecting        a local management tool. The local management tool may be used        to access the base station control module and the transport        module via the base station internal LAN in order to configure        them, when the IP router and L2 switch are not yet configured.        Now communication in a non-configured base station is possible        only within the internal LAN of the base station node 300.    -   2. When the base station transport module 302 has received valid        configuration data (e.g. using the local management tool), the        valid configuration data contains, among other parameters,        filtering settings for the boundary port(s) of the L2 switch in        order to block all the Ethernet frames that contain a        destination (DST) address in which the bits defined for Cabinet        ID are zeroes. Now the base station node forms a VLAN zone with        a private link layer address space. Based on the received        configuration data, the base station transport module 302 shall        also enable the boundary ports in the L2 switch physical        interfaces in order to allow extending the L2 switched local        area network 310 outside the base station node 300, such as        connecting more L2 switched devices to the LAN.    -   3. The base station control module 304 may assign a        predetermined “well-known” link-local IPv4 and IPv6 addresses        for its OA&M interface. These addresses may be used temporarily        for Cabinet ID discovery (location detection) by the other base        station modules 305, 306, 307.    -   4. The other base station modules 305, 306, 307 assign a        temporary link layer address (Ethernet MAC Identifier) from the        private link layer address space (Cabinet ID bits are zeroes)        during initial startup that shall be used only for Cabinet ID        discovery.

The second of the above conditions has to be met in the base stationtransport module 302 because the IP hosts of the base station modules305, 306, 307 must perform Cabinet ID discovery with their networkinterface configured for temporary link layer addresses in which CabinetID bits are not set. Otherwise there will be overlapping address problemduring hot inserts of modules i.e. during normal operation of a basestation node when traffic is enabled via the boundary ports of the L2switch. The possibility of setting filters in L2 switches is a standardfeature where the VLAN bridges may filter frames in order to localizetraffic in the Virtual Bridged LAN. The configuration of staticfiltering entries or static VLAN registration entries in a filteringdatabase disallows the forwarding of frames with particular destinationaddresses or VLAN classifications on specific ports.

Base Station Control Module IPv6 Address Autoconfiguration

It is assumed that the base station control module can access theCabinet ID information by some other means than using the Ethernet linksfor physical access. Thus, only the base station control module is ableto create its complete link layer and IPv6 link-local addresses withoutperforming the Cabinet ID discovery procedure.

When the base station is powered up, all the hosts shall start up inparallel. All the IPv6 hosts shall perform a IPv6 duplicate addressdetection (DAD) procedure when they initialize their network interfaceas will be explained more in detail below. However, the other hosts thanthe control module cannot complete their IPv6 address autoconfigurationscenario before the control module has configured its network interfaceand is thus able to respond to the messages from the other base stationhosts.

The diagram in FIG. 6 shows how the base station control module maycreate and validate its addresses. In sequence 600, a host in the basestation (“any host”) creates and assigns temporary addresses for itsinterface and initializes its interface to the link. In sequence 602,the base station control module creates and assigns addresses for itsinterface and initializes its interface to the link. Following addressesmay be assigned: link layer address (LLA), such as the Ethernet MAC,based on module HW position and Cabinet ID information, base stationcontrol module link-local IPv6 address (ADDR1) in which the interface IDpart of an IPv6 address may be derived from the Ethernet MAC addressusing EUI-64 format, and base station OA&M “well known” link-local IPv6address (ADDR2) that does not overlap with the addresses that arederived from the Ethernet MAC addresses. After the interfaceinitialization, the base station control module may verify the tentativeaddresses, for example, by performing a standard IPv6 duplicate addressdetection (DAD) scenario for the both tentative addresses, sequences604, 608, 610, 614.

The DAD procedure may be done according to a procedure defined in thedocument RFC 2462 “IPv6 Stateless Address Autoconfiguration” as follows:

-   -   Before sending a neighbor solicitation, sequences 604, 610, the        base station control module's interface joins the all-nodes        multicast address and the solicited-node multicast address of        the tentative address.    -   To check an address, the base station control module sends        neighbor solicitation messages, sequences 604, 610. The        solicitation's Target Address is set to the address being        checked, the IP source is set to the unspecified address and the        IP destination is set to the solicited-node multicast address of        the target address.    -   On receiving Neighbor Solicitation any host will process the        message as follows: if the target address is tentative, and the        source address is a unicast address, the solicitation's sender        is performing address resolution on the target; the solicitation        should be silently ignored, sequences 606, 612.    -   If the base station control module does not receive any replies        (neighbor advertisements) to neighbor solicitations within        certain time, it is sure that the checked address is not used by        some other node connected to the same link.

After successful DAD procedures, the base station control module assignsIP addresses to its interface, sequences 608, 614, as now theseaddresses (ADDR1 and ADDR2) can be determined to be unique. Now the basestation control module is able to send packets via its interface andrespond to address resolutions from the other hosts in the network, suchas the other base station modules.

Any Base Station Host IPv6 Address Autoconfiguration

During the startup the IP hosts in modules other than the base stationcontrol module cannot access them selves the Cabinet ID information.Thus a method is defined in the following for retrieving the Cabinet IDinformation from the base station control module. The method may becarried out without using any higher application level messaging i.e.the procedure may be able to run in a bootstrap code of the modulesoftware. The sequence diagram of FIG. 7 shows how all the other basestation hosts can retrieve Cabinet ID from the base station controlmodule and create and validate their addresses. In sequence 700, thebase station control module autoconfigures its link layer and IPv6addresses first during the startup. The procedure may be the following:

In sequence 702, the base station host creates the temporary addressesfor its interface:

-   -   Link layer Address (Ethernet MAC), for example based on the HW        position of the module in the base station node or derived from        the module serial number, except that the bits reserved for the        Cabinet ID are set to zeroes; and    -   Host Link Local IPv6 Address in which Interface ID part is        derived from the temporary Ethernet MAC address.

Sequence 702 continues by the base station host initializing itsinterface. In sequences 704, 706, the base station host performsstandard IPv6 DAD scenario for its temporary and “tentative address”according to RFC 2462 in similar manner as the base station controlmodule did for its interface.

After successful DAD, in sequence 708 the base station host assigns thetemporary IP address to its interface as now it can be determined to beunique. Now the base station host is able to send packets using thistemporary and “validated” IP address to other hosts via its interface.

Next, in sequences 710-720, the base station host may perform an addressresolution procedure for the BTS OA&M's “well known” IP addressaccording to RFC 2461 “Neighbor Discovery for IP Version 6” in order toretrieve the base station control module's link layer address that issupposed to contain the Cabinet ID information. According to RFC 2461“Neighbor Discovery for IP Version 6 (IPv6)”:

-   -   Address resolution is the process through which a node        determines the link layer address of a neighbor given only its        IP address.    -   When a node has a unicast packet to send to a neighbor, but does        not know the neighbor's link layer address, it performs address        resolution.    -   1. A standard way to trigger the address resolution procedure is        to send some IP packet, such as a ping packet, to a neighbor for        which the IP address is known. In an embodiment, a ping packet        may be sent to the base station OA&M's “well known” address        (sequence 710). When the packet is sent from application layer,        it may queue in an IP stack that creates a neighbor cache entry        in an incomplete state (sequence 711) and transmits a neighbor        solicitation message (sequence 712) targeted to a neighbor,        which in this embodiment is the base station control module. The        neighbor solicitation message for address resolution shall have        the following contents:

Link Layer Addresses:

-   -   Source LLA=base station host's temporary link layer address (MAC        address where Cabinet ID bits are zeroes)    -   Destination LLA=“all nodes” (broadcast). It does not matter if        “all nodes” address is used because the reply from external base        station OA&M(s) will be filtered in the base station transport        module.        IP Fields:    -   Source address: base station host's temporary link local IPv6        address (Cabinet ID bits are zeroes in the Interface ID of the        IPV6 address)    -   Destination address: The “well known” base station OA&M's link        local IPv6 address        ICMP Fields:    -   Target address: The “well known” base station OA&M's IP address        Source link layer address (optional): base station host's        temporary link layer address (MAC address where Cabinet ID bits        are zeroes)

The receiving base station control module processes the neighborsolicitation message as follows (sequence 714):

-   -   If the source address is not an unspecified address and, on link        layers that have addresses, the solicitation includes a source        link layer address option, then the recipient may create or        update the neighbor cache entry for the IP source address of the        solicitation. If an entry does not already exist, the node may        create a new entry and set its reachability state to “stale”.

After any updates to the neighbor cache, the node, which in thisembodiment is the base station control module that has assigned the basestation OA&M's “well known” IP address to its network interface, sends aneighbor advertisement response as described in the following (sequence716):

-   -   A node sends a neighbor advertisement in response to a valid        neighbor solicitation targeting one of the node's assigned        addresses. The target address of the advertisement is copied        from the target address of the solicitation. If the        solicitation's IP destination address is not a multicast        address, the target link layer address option may be omitted.        This is because the neighboring node's cached value must already        be current in order for the solicitation to have been received.        If the solicitation's IP destination address is a multicast        address, the target link layer option is included in the        advertisement. Furthermore, if the node is a router, the router        flag is set to one. Otherwise, the node sets the flag to zero.

The contents of the neighbor advertisement reply message from the basestation control module shall be as follows:

Link Layer Addresses:

-   -   Source LLA=base station control module's link layer address (MAC        address where Cabinet ID bits are set accordingly)    -   Destination LLA=base station host's temporary link layer address        (MAC address where Cabinet ID bits are zeroes). The base station        transport module will block the reply messages from the external        nodes, so only the reply from the local base station control        module of the base station node will be received by the        requesting host.        IP Fields:    -   Source Address: The “well known” base station OA&M's IP address    -   Destination Address: base station host's temporary link local        IPv6 address (Cabinet ID bits are zeroes in the Interface ID of        the IPV6 address)

ICMP Fields:

-   -   R Router flag=0 (the base station control module is a host)    -   S Solicited flag=1 indicating that the advertisement was sent in        response to a neighbor solicitation    -   O Override flag=1 indicating that the advertisement should        override an existing cache entry and update the cached link        layer address    -   Target Address: The “well known” base station OA&M's IP address        i.e. same as the Target Address Field in the previous Neighbor        Solicitation message    -   Target link layer address option: The base station control        module's link layer address in which the Cabinet ID bits are set        accordingly (the receiving node's IP stack shall insert this        value in the cache).

When a neighbor advertisement response is received in the base stationhost, its contents, including the link layer address is stored into theneighbor cache, neighbor is marked with a status “reachable” (sequence715) and the queued ping packet is transmitted (sequence 718). It shouldbe noted that the neighbor solicitation message 712 might be received inall base station control modules in other base station nodes that areconnected to the same L2 switched network. However, in this case thebase station host shall receive just one neighbor advertisement responsefrom the local base station control module as the responses from theother base station nodes that are targeted to temporary link layeraddresses (with Cabinet ID bits zeroes) will be blocked in the L2 switchof the base station transport module.

The base station control module will reply to the ping (sequence 720).In this embodiment, the Cabinet ID information is now available in thelink layer address (LLA) field of the neighbor cache entry for the basestation OA&M's “well known” address. In sequence 722, the host reads theLLA from the neighbor cache, resolves the Cabinet ID and updates itsaddresses accordingly and initializes its Ethernet Interface and IPstack with new tentative addresses. The address is tentative until itsuniqueness is verified. In sequences 724, 726, the host performs aduplicate address detection (DAD) for its new IP address according toRFC 2462. After a successful DAD procedure, in sequence 728, the hostvalidates its final IP address in which also the Cabinet ID bits are setaccordingly.

Now the base station host is able to start communicating at applicationlevel with other hosts in the network using its link layer and IPv6 LinkLocal Addresses that are unique within the scope of the L2 switchednetwork.

It is to be noticed that the above presented scenario describes anexample of a successful address configuration case. For example, if thebase station control module has not completed its addressautoconfiguration procedure, the “any hosts” should repeat the steps710-712 until a response is received. In an embodiment, the IP stack maygive indication to the upper layers, such as “Destination isunreachable”. Considerations for a base station module hot insert in aL2 switched network.

When a new base station module is hot inserted into a base station node,which is connected to a L2 switched network with multiple base stationnodes, it must discover its local base station control module in orderto register itself to its correct “Master” and to autoconfigure uniqueaddresses within the scope of the L2 switched network with the correctCabinet ID correspondingly.

The new hot inserted base station module may apply the same “Any basestation IPv6 Host Address Autoconfiguration” procedure as it isdescribed earlier for the initial base station node startup when thefollowing conditions are met:

-   1. The base station control module has assigned for itself a base    station OA&M “well known” link local IPv6 address that is known by    all the base station modules (hard coded).-   2. The scope of the link layer addresses (MAC) with Cabinet ID bits    being zero is limited to cover only the local LAN segment of the    base station node i.e. a VLAN zone is configured into the L2 switch    of the base station transport module.-   3. A new hot inserted base station module discovers its local base    station control module using the base station OA&M's “well known”    link local IPv6 address. An address resolution procedure is    performed such that a new base station module sends an unicast    solicitation for requesting the link layer address of the local base    station control module (Ethernet MAC) that is supposed to include    the Cabinet ID information.

As the result of the successful “Any base station IPv6 Host AddressAutoconfiguration” procedure”, the hot-inserted base station module hasdiscovered its controlling base station control module, the cabinet inwhich it is located physically, and is able to communicate using theunique IPv6 link local addresses within the scope of the L2 switchednetwork.

Basic Scenario for IPv4 Address Autoconfiguration During the 1st BaseStation Startup

In an embodiment, the base station module may be adapted to the IPv4instead of IPv6. The base station modules that will become IPv4 hostspreferably assign their IPv4 addresses using the DHCP. This is becauseIPv4 addressing allows connecting only a limited amount of hosts in bneIP subnet and only the DCHP provides means for managing thepre-configured addresses in the IP subnet. Now It is important to assignunique link layer addresses (MAC) in each base station host to be uniquewithin the scope of the L2 switched network, as the IPv4 addresses canno longer be created using the same rules as in the IPv6 case.

The L2 switched LAN that comprises of one IP subnet should contain aDHCP server that may be located at the base station transport modulethat provides an IP router function i.e. the base station transportmodule 302 of the “root” base station node 300 in FIG. 3.

When the base station transport module 302 has not received itsconfiguration data, the DHCP server may be started using a pool ofprivate IPv4 addresses on default (e.g. 192.168.255.01-192.168.255.15).

When the base station transport module has received the configurationdata, the DHCP server can be configured to have another pool of publicIPv4 addresses (or addresses from another private range e.g. 10.x.x.x)reserved for the hosts in this IP subnet according to a detailed IPnetwork plan. As the host ID portion of an IPv4 address is only few bitslong, they cannot be assigned based on the same rules as in the 64-bitlong interface IDs of IPv6 addresses. Thus, all the IPv4 hosts,including the base station control modules, will get their IP addressesfrom the DHCP server based on rules configured in the DHCP server.

Any Base Station Host IPv4 Address Autoconfiguration

In order to avoid overlapping link layer addresses, the host's linklayer address (Ethernet MAC Identifier) is assigned using the same rulesas in the IPv6 case.

Now the other base station modules than the base station control moduleshould receive the link layer address of its local base station controlmodule in order to resolve the Cabinet ID. This link layer address canbe resolved by using a “well known” IPv4 address for the base stationOA&M function, which in this embodiment is a private IPv4 address.

In IPv4, all the hosts, including the base station control module, mayassign their IPv4 addresses using a standard DHCP procedure. The otherbase station modules may use the address resolution protocol (ARP) fordiscovering the cabinet ID bits to be used in the link layer addresses.This is explained in detail in the following.

The diagram of FIG. 8 shows an IPv4 address autoconfiguration scenariousing the DHCP in accordance with the document RFC2131 “Dynamic HostConfiguration Protocol”:

A DHCP server configures an IP address pool, in sequence 800. Insequence 802, an IPv4 module (“any host”) may create a temporary LLAbased on the module HW position information in which the bits reservedfor the Cabinet ID are zeroes in a similar way as in the IPv6 case. Themodules that cannot detect their physical location are an exception.Their temporary LLA may be derived from the module serial number,instead of using the HW position (lowest order bits), and including theCabinet ID bits that are zeroes.

The any host makes a boot request (sequence 804) and gets a boot reply(sequence 806) from the DHCP server. In sequence 808, the any host sendsa DHCP request. The DHCP server leasing the IP address to the requestinghost may store the IP address in the non-volatile memory of the DHCPserver. The IP address is sent to the any host, in sequence 812, and theIP address is assigned to an interface of the any host, in sequence 814.In the subsequent restarts, the any host may assign the same IP addressfor its interface unless it detects that it is placed in a different HWposition or in a different base station node.

When the base station module “any host” has assigned its IPv4 address,it discovers the link layer address of the local base station controlmodule in order to obtain the Cabinet ID information.

In IPv4 the “Address Resolution Protocol” (ARP) described in thedocument RFC 826 “An Ethernet Address Resolution Protocol” can be usedto resolve the link layer address of another host when its IPv4 addressis known. The ARP scenario illustrated in FIG. 9 is analogous with IPv6address resolution procedure.

The base station host can initiate an address resolution procedure(sequence 900) by sending e.g. a ping packet to base station OA&M's“well known” IPv4 address (sequence 902).

As a result of the ARP procedure (sequences 904, 906), the base stationcontrol module's LLA with Cabinet ID information can be read from theARP table of the host's IP stack (sequence 907).

The queued ping request is transmitted to the base station controlmodule (sequence 908). While a reply to the ping is received from basestation control module (sequence 910), the any base station module shallcreate its permanent link layer address in which the bits reserved forthe Cabinet ID are set accordingly (sequence 912). When the ARP iscompleted, the base station module “any host” re-initializes itsinterface using this new LLA and the IPv4 address that was assignedearlier using the DHCP.

Now the base station module “any host” is able to start communicating atan application level with the other hosts in the base station using itsunique LLA and IPv4 addresses within the scope of the L2 switchednetwork.

Based on the above, an embodiment of the invention may be summarized asfollows. An ARP request in an “any host” is sent by using a temporarylink layer address (LLA) in which the bits reserved for the Cabined IDare zeroes. If there are multiple base station nodes connected to the L2switched network, all the base station control modules will receive thisARP request (broadcast message) and they will respond with an ARP reply.However, in the ARP reply message, the destination address at the linklayer, i.e. in the Ethernet frame, is the temporary LLA of the “anyhost” having zeroes in the predefined Cabinet ID bits. Thus, the L2switch of the transport module, which is set to block the Ethernetframes with a LLA having zeroes in the Cabinet ID bits from the boundaryports of the transport module, will block the frame, i.e. discards it.This means that the “any host” will receive the ARP reply only from itslocal base station control module located physically inside a boundaryset in the L2 switch. In this way, the “any host” is able to discoverits master, i.e. the local base station control module in the same basestation node with the “any host”, and to resolve the Cabinet ID.

Although the invention has been described in the context of particularembodiments, there are several variations and modifications which may bemade to the disclosed solution without departing from the scope of thepresent invention as defined in the appended claims. For example, themethod of the invention may be used for any other telecommunicationequipment having an internal local network, which may become part of anIP transport network. Base station has been used herein only forillustrative purposes and for the simplicity of the presentation.

1. A method for configuring addresses in a packet switched datacommunication system, the method comprising: providing a logical networkwith at least two network elements, a network element of the at leasttwo network elements comprising at least one sub-element; configuring atemporary address for an interface of a sub-element of the at least onesub-element; retrieving an identifier of the network element; anddefining an address for the interface of the sub-element by includingthe identifier of the network element to the temporary address.
 2. Amethod according to claim 1, wherein the configuring step comprisesconfiguring a local link layer address for the interface of thesub-element.
 3. A method according to claim 1, wherein the configuringstep comprises configuring the temporary address for the interface ofthe sub-element based on hardware location information in the networkelement.
 4. A method according to claim 1, wherein the configuring stepcomprises configuring the temporary address for the interface of thesub-element based on a module identifier of the sub-element.
 5. A methodaccording to claim 1, further comprising providing a control sub-elementconfigured to access the identifier of the network element without aneed to communicate with other network elements.
 6. A method accordingto claim 5, further comprising storing the identifier of the networkelement in a memory of the control sub-element.
 7. A method according toclaim 5, wherein the retrieving step comprises retrieving the identifierof the network element from the control sub-element.
 8. A methodaccording to claim 1, wherein the retrieving step comprises retrievingthe identifier of the network element using the temporary address as aunique address to carry out an automatic address resolution procedurelocally in the network element.
 9. A method according to claim 1,wherein the step of defining the address comprises defining a networklayer address for the interface of the sub-element.
 10. A methodaccording to claim 1, further comprising blocking, inside an networkelement, all data packets lacking the identifier of the network element.11. A method according to claim 1, further comprising enabling theinterface of the sub-element for network element external communicationat the earliest when the address for the interface of the sub-element isdefined.
 12. A method according to claim 1, further comprisingretrieving a network portion identifying the logical network andcontinuing the address configuration by including the network portion tothe address of the interface of the sub-element.
 13. A method accordingto claim 1, wherein the providing step comprises providing a layer 2switched local area network with at least two transceiver networkelements, a transceiver network element of the at least two transceivernetwork element comprising a control module and at least one othermodule.
 14. A computer program comprising program code means forperforming any of the steps according to claim 1 when program code isrun on a computing means.
 15. A network element comprising: at least onesub-element; a configuring means configured to configure a temporaryaddress for an interface of a sub-element of the at least onesub-element and to define an address for the interface of thesub-element by including an identifier of the network element retrievedby a retrieving means; and the retrieving means configured to retrievethe identifier of the network element.
 16. A network element accordingto claim 15, wherein the configuring means is configured to configure alocal link layer address for the interface of the sub-element.
 17. Anetwork element according to claim 15, wherein the configuring means isconfigured to configure the temporary address based on hardware locationinformation of the sub-element in the network element.
 18. A networkelement according to claim 15, wherein the configuring means isconfigured to configure the temporary address based on a moduleidentifier of the sub-element.
 19. A network element according to claim15, further comprising a control sub-element configured to access theidentifier of the network element without a need to communicate withother network elements.
 20. A network element according to claim 19, thecontrol sub-element comprising a memory configured to store theidentifier of the network element.
 21. A network element according toclaim 19, wherein the retrieving means is configured to retrieve theidentifier of the network element from the control sub-element.
 22. Anetwork element according to claim 15, wherein the retrieving means isconfigured to retrieve the identifier of the network element using thetemporary address as a unique address to carry out an automatic addressresolution procedure locally in the network element.
 23. A networkelement according to claim 15, wherein the configuring means isconfigured to configure a network layer address for the interface of thesub-element.
 24. A network element according to claim 15, furthercomprising blocking means configured to block, inside the networkelement, all data packets lacking the identifier of the network element.25. A network element according to claim 15, wherein the retrievingmeans is further configured to retrieve a network portion identifying alogical network and continuing an address configuration of theconfiguring means by including the network portion to the address of theinterface of the sub-element.
 26. A network element according to claim16, wherein the link layer address is based on a 48-bit media accesscontrol identifier format.
 27. A network element according to claim 23,wherein the network layer address is one of a link-local InternetProtocol version 6 address based on an EUI-64 identifier and an InternetProtocol version 4 address using a dynamic host configuration protocol.28. A network element according to claim 15, the network element being atransceiver network element and comprising a control module and at leastone other module.
 29. A communication system comprising: a logicalnetwork comprising at least two network elements, a network element ofthe at least two network elements comprising at least one sub-element; aconfiguring means configured to configure a temporary address for aninterface of a sub-element of the at least one sub-element and to definean address for the interface of the sub-element by including anidentifier of the network element retrieved by a retrieving means; theretrieving means adapted to retrieve the identifier of the networkelement.